Improvement of haze ratio of DC (direct current)-sputtered ZnO:Al thin films through HF (hydrofluoric acid) vapor texturing

The textured ZnO:Al films are used to enhance light trapping in thin film solar cells. The wet etch process is used to texture ZnO:Al films by dipping in diluted acidic solutions such as HCl (hydrogen chloride acid) or HF (hydrofluoric acid). During this process, the acidic solution can damage the glass substrate, which could then be difficult to apply for the inline mass production process since this process needs to be performed outside the chamber. In this paper we report a new technique to control the surface morphology of DC-sputtered ZnO:Al films. The ZnO:Al films are textured with vaporized HF formed by mixing the HF with an H2SiO3 solution. We achieved a high haze value of 74.6% at a 540 nm wavelength by increasing the etching time and HF concentration. A haze value of about 58% was achieved at a 800 nm wavelength when vapor texturing was used. The ZnO:Al film texture by HCl had a haze ratio of about 9.5% at 800 nm and less than 40% at 540 nm. In addition to a low haze ratio, in the texturing by HCl it was very difficult to control etching and to keep reproducibility due to its very fast etching speed.